In temperate and boreal mixedwood forests of eastern North America, partial disturbances such as insect outbreaks and gap dynamics result in the development of irregular forest structures. From a forest ecosystem management perspective, management of these forests should therefore include silvicultural regimes that incorporate medium- to high-retention harvesting. We present 12-year results of a field experiment undertaken to evaluate the effects of variable retention harvesting on stand structure, recruitment, and mortality. Treatments were gap harvesting (GAP), diameter-limit harvesting (DL), careful logging (CL), and careful logging followed by scarification (CL + SCAR), and an unharvested control. Although post-harvest basal area in the GAP treatment was significantly lower than that of controls, it maintained a diameter distribution profile and densities of balsam fir regeneration similar to those of pre-harvest conditions. Lower retention treatments (DL, CL, and CL + SCAR) tended to favor regeneration of pioneer, shade-intolerant species. Except for black spruce (for which mortality was highest in DL), stem mortality was similar among harvesting treatments. From an ecosystem management perspective, this study suggests that gap harvesting can maintain, in the short term, forest stand composition and structure similar to unharvested forests, and could be used where management objectives include the maintenance of late successional forest conditions.

Mixed species stands present a number of opportunities and challenges to forest managers. Boreal mixedwood stands in eastern Canada are often characterized by a canopy of shade intolerant aspen (Populus tremuloides) with more shade tolerant conifers in the sub-canopy layers. Because the aspen and conifers often attain optimal merchantable sizes at different moments, there is an interest in developing silvicultural practices toremoval of aspen and favour accelerated growth of residual conifers. We tested three partial harvesting treatments in mixed aspen - white spruce (Picea glauca) stands in which different proportions of aspen (0, 50, 65 and 100% basal area) were removed. Ten years after treatments, 72 spruce stems destructively sampled for stem analysis. Using linear mixed effect models, we analyzed growth as a function of treatment intensity, time since treatment, social status, pre-treatment growth rate, and neighbourhood competition. Relative to control stands, radial and volume growth responses were detected only in the extreme treatment of 100% aspen removal. In relative terms, suppressed trees showed the greatest magnitude of cumulative growth increase. Growth response was proportional to pre-treatment growth rate and, among neighbouring trees, only coniferous neighbours had a negative effect on white spruce growth.

This study examines tree and stand response to a gradient of commercial thinning intensities and nitrogen fertilization (200 kg N ha?1) in nine jack pine (Pinus banksiana) stands of Eastern Canada over a period of 14 years. Thinning intensity ranged from 0% basal area removal in control plots to 64% in thinned plots. Tree diameter increment, absolute and relative volume increment and mean volume increased with thinning intensity and were higher in fertilized plots. Individual tree response depended on tree diameter, with smallest trees exhibiting highest relative volume increment to thinning intensity. Stand basal area increment was positively associated to initial stand basal area and negatively to stand age. In thinned and fertilized plots, stand volume increment was higher and natural mortality lower than in fertilized only and unfertilized control plots over the 5–14 year period after thinning. However, the positive effect of fertilization on tree volume increment decreased with thinning intensity. Despite positive individual tree growth responses to thinning and fertilization, residual stand volume increment decreased with increased thinning intensity in both fertilized and unfertilized plots. While total cumulative stand volume (harvested + residual) also decreased with thinning intensity in unfertilized plots, comparable total volumes were observed in fertilized + thinned and unthinned control plots. Nitrogen fertilization in the years following commercial thinning enhanced the benefit of thinning on these relatively poor sites by increasing tree diameter growth, lowering mortality, and increasing total stand merchantable volume compared to unfertilized thinned stands.

In the current context of forest ecosystem management, partial harvesting has been proposed as a silvicultural tool to augment forest variability on managed landscapes and to accelerate the development of structural and compositional attributes of old-growth/late successional stands. The aims of this paper were to (1) identify and characterize, based on the literature, the structural attributes of old-growth aspen-dominated stands in the North American boreal mixedwood forest, and (2) examine the short-term potential of partial harvesting in aspen-dominated stands to accelerate stand development toward these old-growth characteristics. Two stand types – pure aspen (93% aspen basal area) and mixed aspen (81% aspen basal area) – were monitored over a 12-year post-treatment period. The scientific literature suggests that compared to pure, even-aged premature or mature stands, old-growth aspen stands have lower merchantable stem densities and basal area, more large aspen stems, higher stem size variability, more than one cohort of trees, greater percentage area occupied by gaps, higher expanded gap area, and more and larger snags and downed wood. In addition, old-growth aspen mixedwoods characteristically have more shade-tolerant conifers in understory and overstory layers than younger, mature stands. Results of this study indicate that light thinning from below (33% basal area removal) applied in pure aspen stands successfully retained most of the structural attributes of mature aspen stands, but did not generally “accelerate succession” toward old-growth traits in the 12-year time interval since treatment. A dispersed free thinning (45% basal area removal in all merchantable size classes) applied in mixed aspen stands showed its potential to “accelerate succession” by creating canopy gaps similar to old-growth aspen stands and by promoting recruitment of both tolerant and intolerant tree species. Two high intensity partial harvesting treatments, a thinning from above of 61% basal area in pure aspen stands and 400 m2 gap cuts (54% basal area removal) in mixed aspen stands may set back stand development by disproportionally favoring recruitment and growth of intolerant hardwood species.

Background

The development of forestry as a scientific and management discipline over the last two centuries has mainly emphasized intensive management operations focused on increased commodity production, mostly wood. This “conventional” forest management approach has typically favored production of even-aged, single-species stands. While alternative management regimes have generally received less attention, this has been changing over the last three decades, especially in countries with developed economies. Reasons for this change include a combination of new information and concerns about the ecological consequences of intensive forestry practices and a willingness on the part of many forest owners and society to embrace a wider set of management objectives. Alternative silvicultural approaches are characterized by a set of fundamental principles, including avoidance of clearcutting, an emphasis on structural diversity and small-scale variability, deployment of mixed species with natural regeneration, and avoidance of intensive site-preparation methods.

Methods

Our compilation of the authors’ experiences and perspectives from various parts of the world aims to initiate a larger discussion concerning the constraints to and the potential of adopting alternative silvicultural practices.

Results

The results suggest that a wider adoption of alternative silvicultural practices is currently hindered by a suite of ecological, economic, logistical, informational, cultural, and historical constraints. Individual contexts display their own unique combinations and relative significance of these constraints, and accordingly, targeted efforts, such as regulations and incentives, may help to overcome specific challenges.

Conclusions

In a broader context, we propose that less emphases on strict applications of principles and on stand structures might provide additional flexibility and facilitate the adoption of alternative silvicultural regimes in a broader set of circumstances. At the same time, the acceptance of alternative silvicultural systems as the “preferred or default mode of management” will necessitate and benefit from the continued development of the scientific basis and valuation of a variety of ecosystem goods and services. This publication is aimed to further the discussion in this context.

Multi-cohort-based forest management has been proposed as a strategy to conciliate wood supply and biodiversity conservation objectives. At the stand-level, the approach involves using partial harvesting to generate structurally complex stands, notably in terms of tree age, size and species mixtures, conditions that are not easily integrated into yield tables. Using SORTIE-ND, a spatially explicit stand dynamics model, we simulated 100-year development patterns following different partial harvesting treatments in two trembling aspen (Populus tremuloides Michx)-dominated stands in eastern Canada, one 76-year old (pure aspen) and the other 90 years old (mixed aspen). The two stand types differed primarily in the nature of their understory: pure aspen stands had little advance conifer growth and a dense understory of a woody shrub species whereas mixed aspen stands were characterized by a dense regeneration layer of shade-tolerant conifers. To do this, we first evaluated model performance using short (12 years) and long (168 years) term empirical data. We then modelled stand dynamics following a range of simulated partial harvesting treatments of different intensities (33, 61 and 80% basal area removal), and gap sizes (400, 900 and 1600 m2). Following mortality of the first cohort of aspen, simulations projected dominance of conifer species, white spruce in particular, in unharvested controls of pure aspen stands and balsam fir in mixed aspen stands. Aspen recruitment increased with intensity of partial harvesting. All gap treatments and the 80% dispersed harvesting favored recruitment of aspen over conifer species. After 100-year simulation runs, the 1600 m2 gap treatment resulted in highest stand basal areas, 38.0 and 34.1 m2 ha?1, of which 18% and 28% consisted of intermediate- to shade-tolerant conifer species in pure aspen stands and in mixed aspen stands, respectively. Concerns surrounding partial harvesting have tended to focus on absolute retention levels and standing residence times of trees; however, our results demonstrate that both stand structure and timber production rates are influenced not only by retention levels after partial harvesting but also by spatial configuration of the residual trees. We identified several model functions that are likely responsible for divergences between empirical conditions and those simulated by SORTIE-ND for the boreal mixedwood and suggest specific empirical studies to improve parameter functions of this modelling tool.

Boreal mixedwood management has shifted from a relatively narrow focus on commercial wood supply to greater consideration of the natural dynamics and multiple ecological services. This recognition has generated interest in ecosystem management approaches that include diversifying and adapting silvicultural practices, including partial harvesting. The effects of partial harvesting on stand dynamics was assessed over a 12-year period in trembling aspen (Populus tremuloides Michx.) dominated stands in northwestern Quebec, Canada. Four treatments were tested: clearcuts (100% basal area (BA) removal); 1/3 partial cut (1/3 PC, 33% BA removal using low thin); 2/3 partial cut (2/3 PC, 61% BA removal using high thin) and controls (0% removal). Aspen sapling recruitment was directly affected by harvesting intensity with 1/3 and 2/3 partial cuts generating 5% and 56%, respectively, of aspen sapling densities in clearcuts. Aspen sapling recruitment increased continuously following clearcut and partial cut treatments with no significant mortality in the sapling layer over the 12-year period. Recruitment of conifer saplings also increased with time and was significantly higher in the two partial cuts than in the clearcut treatment. Twelve years after treatments, mortality of residual aspen stems (?10 cm DBH) reached 250 stems ha?1 12 yr?1 in controls, compared to 106, and 170 stems ha?1 12 yr?1 in 1/3 PC, and 2/3 PC stands, respectively. Initially (1–3 years after treatments), higher overstory aspen mortality was associated with the 2/3 PC treatment. Aspen mortality was strongly associated with small-sized merchantable stems (10–19.9 cm DBH) regardless of treatment. Both partial harvesting treatments had the effect of maintaining mountain maple (Acer spicatum Lamb.), a shade-tolerant, high woody shrub, at densities similar to those in control stands whereas recruitment of mountain maple saplings was negligible in clearcuts due to high aspen recruitment. Our results indicate that (i) heavy-high partial harvesting promotes sapling recruitment of both aspen and conifers when advance regeneration of the latter is present, (ii) because aspen sucker response can be controlled by varying harvesting intensities and stem selection, it is possible to create a range of mixedwood conditions, depending on whether mixed, structurally complex or more regular aspen-dominated stands are desired, and (iii) on rich mixedwood sites, tall woody shrubs could hinder desirable partial harvesting outcomes.

Variable retention harvesting, with a focus on maintaining biological legacies on managed landscapes, has been practised in the trembling aspen (Populus tremuloides Michx.) dominated boreal mixedwood forests for about two decades. However, little attention has actually been given to the growth response of aspen to partial harvesting. This is the first study to report on tree-level volume growth response of aspen after partial or variable retention harvesting in the Canadian boreal forest. During the winter of 1998–1999, an uncut control, clearcut and two partial harvesting treatments – 1/3 partial cut (1/3PC, 33% BA removal using low thin); 2/3 partial cut (2/3PC, 61% BA removal using high thin) – were applied in 75 year old aspen-dominated mixedwood stands in a complete randomized block design. Twelve years after treatment application, 27 dominant and 27 co-dominant trees were collected from unharvested controls and the two partial cut treatments for stem analysis. Annual volume increment (AVI) of individual stems was analyzed as a function of treatment, tree social status, pre-treatment growth, time since treatment application (1–12 years) and neighborhood competition. The latter was estimated using a variety of neighborhood competition indices (NCI). There was no evidence of initial growth stagnation after partial harvesting applications. Only the most severe treatment of partial harvesting (2/3 PC) resulted in an increase in volume increment relative to trees in control stands. Annual increase in volume in the 2/3 partial cut was 25.6% higher than controls over 12 years. AVI of dominant trees was higher by 16.2 dm3 yr?1 than that of co-dominants and was proportional to pre-treatment volume growth. No interaction between treatment and social status or pre-treatment growth was observed. The overall results indicate that competition for resources in these stands is essentially size symmetrical. These results should contribute to the development of silviculture prescriptions that aim to maintain both stand productivity and biological legacies.

Over the last 25 years, greater understanding of natural dynamics in the boreal forest has led to the integration of forest ecosystem management principles into forest policy of several Canadian provinces and, in turn, to greater interest in developing silvicultural treatments that are grounded in natural stand-level dynamics – often referred to as natural disturbance-based silviculture. As a result, alternative silvicultural practices including variants of partial cutting are increasingly being applied in the boreal forest as an approach to balancing economic and ecological management objectives. While the numerous benefits of partial cutting reported in the literature are acknowledged, the objective of this paper is to provide an overview of factors or constraints that potentially limit the application of these practices in boreal Canada in the context of forest ecosystem management and natural disturbance-based silviculture. Among constraining factors, numerous studies have reported elevated mortality rates of residual stems following partial cutting, initial growth stagnation of residual trees, problems related to recruitment of desirable species and, on certain flat or lowland sites, risks of long-term decline in site and stand productivity. A number of operational challenges to partial cutting in the boreal forest are also presented and several avenues of research are proposed.

Renewed interest in biomass harvesting has underscored the need for ecologically relevant thresholds and empirical validation of species responses for deadwood retention if biodiversity is to be preserved in managed landscapes. We experimentally reduced volumes of downed deadwood in clear cut jack-pine stands in Western Quebec, Canada and then monitored changes in spider and ground beetle assemblages 1 and 2-years following biomass removal as well as in uncut stands. We reduced volume of downed deadwood by (1) removing residual deadwood placed on machine corridors during the initial harvest of the stand to minimize soil compaction and (2) removing all residual deadwood material throughout the experimental plots. Ground beetle and spider assemblages from deadwood depleted plots were then compared with those in clearcut plots where no additional biomass had been removed and with uncut stands to assess the incremental effect of overstory removal and subsequent biomass removal using multivariate regression trees. We identified 13,822 individual arthropods representing 177 species. We observed differences in species assemblages attributable to the effects of overstory removal (35% of the explained variance) as well as biomass removal, particularly between plots with intensive removal of biomass and those with no additional or moderate removal of biomass (11% of the explained variance). As expected we observed a range of individual species response patterns. Of particular concern were species that experienced incrementally negative effects of overstory and biomass removal and those that were strongly promoted by biomass removal. These species showed responses atypical of those observed following clear cutting and may fall outside both the range of natural variability observed in this region as well as the range of current forest management intensity practiced in North America.

Partial harvesting has been proposed as a key aspect to implementing ecosystem management in the Canadian boreal forest. We report on a replicated experiment located in boreal mixedwoods of Northwestern Quebec. In the winter of 2000–2001, two partial harvesting treatments, one using a dispersed pattern, and a second, which created a (400 m2) gap pattern, were applied to a 90-year-old aspen-dominated mixed stand. The design also included a clear cut and a control. Over the course of the following eight years, live tree, coarse woody debris, regeneration and ground beetles were inventoried at variable intervals. Our results indicate that all harvesting treatments created conditions favorable to balsam fir (Abies balsamea) sapling growth and trembling aspen (Populus tremuloides) sapling recruitment. However, balsam fir and trembling aspen regeneration and ground beetles response to gap cuts were closer to patterns observed in clear cuts than in dispersed harvesting. The underlying reasons for these differing patterns can be linked to factors associated with the contrasting light regimes created by the two partial harvesting treatments. The study confirms that partially harvesting is an ecologically sound approach in boreal mixedwoods and could contribute to maintaining the distribution of stand ages at the landscape level.

Le maintien de la structure spatiale des forêts est de plus en plus reconnu comme un outil de gestion pertinent pour le maintien de la biodiversité. Dans cette étude, nous utilisons des cartes d'inventaire forestier datant de 1965, 1972, 1983 et 1994 pour décrire la structure spatiale historique récente du paysage à la Forêt d'enseignement et de recherche du Lac Duparquet dans le nord-ouest du Québec, Canada. Le couvert forestier fut décrit en utilisant un modèle de « cohorte » de développement des peuplements forestiers basé sur la composition et d'autres attributs de peuplement. Les peuplements forestiers contigus ayant été associés à la même classe de cohorte furent agglomérées en « patches » de cohorte relativement uniformes. La structure spatiale du paysage fut définie en utilisant quatre indices de paysage: la proportion du paysage occupée, la taille moyenne, la distance moyenne du plus proche voisin et la forme moyenne pour les agglomérations de peuplements d'une même cohorte. Les agglomérations de peuplements de la cohorte 1 étaient soit petites ou grandes et avaient des formes complexes. Les agglomérations de peuplements de la Cohorte 2 étaient petites, dispersées et avec une forme simple. Les peuplements de la Cohorte 3 constituaient la matrice du paysage et se trouvaient en petites et grandes agglomérations. Notre classification de polygones forestiers en cohortes a été validée en comparant la proportion du territoire occupée par chaque cohorte dans deux feux (1923 et 1760) qui ont façonné ce territoire. Des cibles théoriques locales visant le maintien de la structure des cohortes à travers le paysage ont été ensuite élaborées à partir des caractéristiques historiques du paysage.

Le 17 juillet 2006, des vents d’une très grande force ont causé un chablis allant du sud du Témiscamingue jusqu’en Mauricie, soit plus de 21 000 ha de forêt renversée. Ce chablis a offert une occasion unique d’étudier les effets sur la composition et la structure forestière que peut avoir cette perturbation méconnue de la zone tem-pérée nordique. Nous avons donc mis en place cette étude afin d’évaluer : 1) l’importance des traits fonctionnels des espèces sur la vulnérabilité d’un arbre à céder sous la force du vent selon que le chablis est sévère ou modéré, et 2) l’utilisation des microsites post-chablis dans le recrutement des espèces arborescentes. En som-me, nous avons observé que les arbres sont plus vulnérables au chablis sévère lorsqu’ils sont résineux et/ou intolérant à l’ombre, et/ou lorsqu’ils ont un DHP supérieur à 20 cm et/ou des racines superficielles, tandis que les arbres intolérants à l’ombre et/ou résineux sont plus facilement affectés par le chablis modéré. De toutes les es-pèces, le peuplier à grandes dents est la plus vulnérable aux chablis sévères et modérés. Les probabilités de se déraciner plutôt que de casser sous un chablis sévère augmentent en fonction du DHP. Finalement, les microsi-tes de puits et de monticules créés lors d’un déracinement ne semblent pas jouer un rôle déterminant dans le recrutement des espèces, à l’exception du bouleau jaune. En conclusion, les chablis ont une tendance à faire accélérer le processus de succession ainsi qu'à faire augmenter l’abondance de bouleau jaune.

L’objectif de cette recherche, réalisée en forêt mélangée au Témiscamingue, était de comparer une forêt dynami-sée par des perturbations naturelles partielles avec deux types de coupe partielle : une coupe de succession (CS) et une coupe avec protection des petites tiges marchandes (CPPTM). Les aspects suivants étaient étudiés : 1) la diversité structurelle des peuplements résiduels; 2) la croissance des arbres résiduels; 3) la composition de la régénération et 4) la croissance des gaules de sapin baumier. Les résultats démontrent que la CS et la CPPTM maintiennent une diversité structurelle et une densité d’espèces tolérantes à l’ombre semblables à celles que nous avons mesurées en forêt naturelle partiellement perturbée. À la suite de la CS et de la CPPTM, les es-pèces étudiées, à l’exception de l’épinette noire, avaient un accroissement radial important, et même supérieur à celui mesuré en forêt naturelle. En conclusion, les deux traitements sylvicoles évalués présentent un intérêt po-tentiel pour l’industrie forestière, car ces deux coupes permettent de maintenir une diversité structurelle et une composition en espèces qui équivalent à celles de la forêt dynamisée par des perturbations naturelles partielles.

Les conditions lumineuses jouent un rôle important dans la dynamique forestière et sont directement affectée par les interventions sylvicoles. L'objectif de cette étude était de déterminer comment les conditions lumineuses du sous-bois d'un peuplement boréal mixte sont affectées par des variations dans l'intensité et le patron spatial de récolte. À l'aide du modèle de simulation SORTIE-ND, nous avons simulé neuf traitements de coupe partielle en combinant trois taux de prélèvement (30 %, 45 % et 60 % de la surface terrière) et trois patrons de récolte (uniforme, par bandes étroites et par trouées). Nos résultats démontrent que la récolte n'augmente pas nécessai-rement la transmission de la lumière en sous-étage d'une façon proportionnelle au taux de prélèvement, le patron spatial de récolte jouant un rôle déterminant. De façon générale, on observe que, pour un même niveau de prélè-vement, un patron de récolte plus agrégé génère des conditions lumineuses plus élevées.

In the context of partial harvesting, adequately managing post-harvest light conditions are essential to obtain a desired composition of tree species regeneration. The objective of this study was to determine how varying the intensity and spatial pattern of harvest would affect understory light conditions in boreal mixedwood stands of northwestern Quebec using the spatially explicit SORTIE-ND light model. The model was evaluated based on comparisons of observed and predicted light levels in both mapped and un-mapped plots. In mapped plots, reasonably accurate predictions of the overall variation in light levels were obtained, but predictions tended to lack spatial precision. In un-mapped plots, SORTIE-ND accurately predicted stand-level mean GLI (Gap Light Index) under a range of harvest intensities. The model was then used to simulate nine silvicultural treatments based on combinations of three intensities of overstory removal (30%, 45% and 60% of basal area) and three harvest patterns (uniform, narrow strips, large gaps). Simulations showed that increasing overstory removal had less impact on light conditions with uniform harvests, and a more marked effect with more aggregated harvest patterns. Whatever the harvest intensity, uniform cuts almost never created high light conditions (GLI > 50%). Gap cuts, on the other hand, resulted in up to 40% of microsites receiving GLI > 50%. Our results suggest that either a 30% strip or gap cut or a 45–60% uniform partial harvest could be used to accelerate the transition from an aspen dominated composition to a mixedwood stand because both types of cut generate the greatest proportion of moderately low light levels (e.g., 15–40% GLI). These light levels tend to favour an accelerated growth response among shade-tolerant conifers, while preventing excessive recruitment of shade-intolerant species. A better understanding of how spatial patterns of harvest interact with tree removal intensity to affect understory light conditions can provide opportunities for designing silvicultural prescriptions that are tailored to species’ traits and better suited to meet a variety of management objectives.

Les peuplements mélangés, caractérisés par une abondance de tiges résineuses prématures croissant sous un couvert dominant de peuplier faux-tremble mature, se prêtent bien à la coupe partielle qui favoriserait la croissan-ce des tiges supprimées et l'établissement de la régénération. Dans cette étude, nous décrivons la réponse initia-le de peuplements soumis à trois types de coupe où on a fait varié l'intensité de la récolte de la surface terrière du tremble par rapport à celle des peuplements témoins. Nous avons ainsi observé que la croissance des tiges inter-médiaires d'épinette blanche était favorisée par la coupe la plus sévère seulement. Après 5 ans, les coupes n'ont pas eu d'effet sur l'établissement et la croissance de la régénération résineuse. Un essai de scarifiage visant à favoriser l'établissement de semis a donc été réalisé. À la suite d'une année semencière, le taux d'établissement des semis d'épinette blanche sur le sol scarifié variait de 125 à 165 semis/m². En dépit de la mortalité élevée d'une grande proportion des semis, une régénération adéquate pourrait être assurée dans la zone scarifiée.

En forêt boréale de l’est du Canada, le terme enfeuillement est généralement réservé au phénomène d’augmentation de la proportion relative de feuillus de lumière, notamment du peuplier faux-tremble (Populus tremuloides), qui survient après coupe forestière. Il est perçu comme un processus qui, bien qu’ayant cours à une échelle locale, a des répercussions à l’échelle régionale. L’objectif de cette étude était de caractériser l’augmentation du couvert de peuplier suite à la coupe totale dans la plaine argileuse de l’Abitibi, dans le nord-ouest du Québec. Les données de 3 inventaires forestiers provinciaux (1970, 1980 et 1990) du ministère des Ressources naturelles et de la Faune du Québec ont été analysées pour 2 régions écologiques, la plaine de l’Abitibi (sous-domaine de la sapinière à bouleau blanc de l’Ouest) et la plaine du lac Matagami (sous-domaine de la pessière à mousses de l’Ouest). Un bilan des transformations qu’a subi le couvert forestier sous l’influence des coupes totales sur près de 3 décennies a été dressé en fonction du temps écoulé depuis la coupe, du dépôt/drainage et de la région écologique. Les résultats montrent que les argiles mésiques sont particulièrement sensibles à l’enfeuillement par le peuplier et que le taux global d’enfeuillement dans la sapinière et la pessière est d’environ 30 % entre les années 1970 à 1990. Par ailleurs, malgré une plus grande abondance de milieux humides et organiques peu propices à l’établissement du peuplier dans la région de la pessière, les 2 régions comparées semblent démontrer la même sensibilité (ou propension) à l’enfeuillement. Sur les sites considérés sensibles, la pessière noire devrait donc faire l’objet de pratiques d’aménagement adaptées visant à limiter l’augmentation de la composante feuillue.

Nous avons quantifié la réponse du tremble à l'éclaircie précommerciale (EPC) dans des conditions pro-pres au sud de l'Abitibi. Trois intensités d'éclaircie (1000, 2000, 3000 tiges/ha) ont été comparées à des peuplements témoins. La réponse initiale des peuplements ainsi que la réponse des tiges résiduelles et de la végétation concurrente à ce traitement ont été évaluées 4 ans après l'application des traitements. Suite à l'EPC, nous observons que la croissance en diamètre du tremble augmente suite à l'éclaircie mais que les trois traitements sont comparables entre eux. Les signes des maladies et les blessures aux arbres étaient rares. Malgré une mortalité élevée dans les peuplements témoins, les surfaces terrières y demeurent toujours supérieures à celles des peuplements traités. Si les tendances observées se main-tiennent, l'éclaircie précommerciale permettrait de réduire l'âge d'exploitabilité tout en augmentant le volume individuel des tiges résiduelles.

In the winter of 1998–1999, two partial harvesting treatments that removed 33% (1/3) and 61% (2/3) of stand basal area were applied to even-aged trembling aspen (Populus tremuloides Michx.) stands and compared with unharvested control stands. Stands in the 1/3 treatment were low thinned, while stands in the 2/3 removal were crown thinned. Coarse woody debris dynamics were assessed during the following 6 years by means of permanent sampling plots and downed wood inventories. Between 1999 and 2004, tree mortality was, respectively, 18%, 17%, and 32% in control stands and 1/3 and 2/3 harvesting treatments. Although total snag density was similar between controls and partial cutting treatments, total snag basal area was significantly higher in controls in 2004. Between 1999 and 2004, net change in aspen snag density was positive for controls and negative for both partial cutting treatments. Partial cutting also exacerbated mortality of small-diameter white birch (Betula papyrifera Marsh.). Downed wood volume increased by 35 m3·ha–1 in controls and by 25 m3·ha–1 in the 2/3 harvesting treatment, while it decreased by 7 m3·ha–1 in the 1/3 harvesting treatment. Coarse woody debris goals can be established in silviculture prescriptions; type, timing, and intensity of partial cutting are crucial to the outcome. © 2007 NRC Canada.

À l’hiver 1998–1999, deux traitements de coupe partielle qui ont prélevé 33 % (1/3) et 61 % (2/3) de la surface terrière ont été appliqués à des peuplements équiennes de peuplier faux-tremble (Populus tremuloides Michx.) et comparés avec des peuplements témoins non traités. Les peuplements dans le traitement 1/3 ont été éclaircis par le bas tandis que les peuplements dans le traitement 2/3 ont été éclaircis par le haut. La dynamique du débris ligneux grossier a été étudiée au cours des 6 années suivant les traitements à l’aide de placettes d’échantillonnage permanentes et des inventaires du bois au sol. Entre 1999 et 2004, la mortalité arborescente a été 18 %, 17 % et 32 %, respectivement, dans les témoins et les traitements 1/3 et 2/3. Bien que les densités totales de chicots soient similaires entre les témoins et traitements de coupe partielle, la surface terrière de chicots (toutes espèces) était significativement plus élevée dans les témoins en 2004. Entre 1999 et 2004, le changement net de la densité de chicots de peuplier a été positif pour les témoins et négatif pour les deux traitements de coupe partielle. Les coupes partielles exacerbent aussi la mortalité des bouleaux à papier (Betula papyrifera Marsh.) de petits diamètres. Le volume du bois au sol a augmenté par 35 m3·ha–1 dans les témoins et par 25 m3·ha–1 dans le traitement 2/3 tandis qu’il a diminué par 7 m3·ha–1 dans le traitement 1/3. Des objectifs spécifiques quant au maintien du débris ligneux grossier peuvent être établis dans des prescriptions sylvicoles; le type, le moment et l’intensité des coupes partielles sont critiques au résultat. © 2007 NRC tous droits réservés.

Abstract : Southern boreal forests dominated by trembling aspen (Populus tremuloides Michx.) are notable for the biological richness of their plant communities. We used 12 plant community and plant functional group indicators to test the hypothesis that natural dynamics-based silvicultural systems better maintain biodiversity in aspen plant communities than conventional clear-cutting. Using CA ordination, box-and-whisker diagrams, and ANOVA, we compared the range of variability of our 12 bioindicators among five experimental stand types of the sylviculture et aménagement forestier écosystémiques (SAFE) project: mature (78 years) uncut; mature 1/3 partial-cut; mature 2/3 partial-cut; young (3 years) unburned clear-cut; young burned clear-cut; and three closely matched aspen stand types of northwest Quebec and northeast Ontario: old (105 years) uncut; young unburned clear-cut; young wildfire. Burned clearcuts partially emulated wildfires by reducing tall shrub abundance and regenerating post-fire specialists, but snags were lacking. The dual disturbance also retarded aspen regrowth and caused a 7-fold increase in non-native plants. Partial-cuts retained most attributes of mature uncut stands, but after 3 years showed little evidence of accelerating development of old stand characteristics. We concluded that SAFE natural dynamics-based silviculture better recreated the range of variability of naturally disturbed aspen plant communities than conventional clear-cutting. Improvements, including alternative burn prescriptions and snag or green tree retention in clearcuts, are nontheless warranted.© 2007 NRC Canada.

Résumé : La forêt boréale méridionale dominée par le tremble (Populus temuloides Michx.) comporte des communautés végétales remarquables par leur richesse biologique. En utilisant 12 indicateurs de communautés végétales et groupes fonctionnels de plantes, les auteurs testent l’hypothèse que des systèmes de sylviculture basés sur leurs dynamiques, assurent une meilleure biodiversité dans les communautés de tremble, que la coupe à blanc conventionnelle. En utilisant l’ordination CA, les diagrammes en boîtes à moustache (box-and-whisker) et le test ANOVA, les auteurs comparent l’amplitude de la variabilité des 12 bioindicateurs au sein des 5 types de parcelles expérimentales du projet sylviculture et aménagement forestier écosystémiques (SAFE) : mature (78 ans) non coupée; mature partiellement coupée au 1/3; mature partiellement coupée au 2/3; jeune (3 ans) coupée à blanc non brûlé; jeune coupée à blanc et brûlée. Ils ont inclus également 3 types de peuplement forestiers de tremble étroitement appariés, du nord-ouest du Québec et du nord-est de l’Ontario; suranné (105 ans) non coupé; jeune coupé à blanc non brûlé; jeune, incendié naturellement. Les peuplements coupés à blanc et incendiés se comparent à ceux issus de feux naturels avec une réduction de l’abondance de grands arbustes et en assurant la régénération par les espèces spécialistes d’après feu, mais les chicots font défaut. La double perturbation retarde également la régénération en tremble et multiplie par 7 l’arrivée d’espèces non indigènes. La coupe partielle retient la plupart des attributs des peuplements matures non coupés, mais montre peu de preuves d’un développement accéléré des caractéristiques des vieux peuplements, après 3 ans. Les auteurs concluent que l’approche SAFE, impliquant une sylviculture basée sur la dynamique naturelle, arrive mieux à recréer l’amplitude de variabilité des communautés de trembles naturellement perturbées, que la coupe à blanc conventionnelle. On obtient des améliorations certaines en incluant des prescriptions de brûlage alternatives et la rétention de chicots et d’arbres verts dans les coupes à blanc. © 2007 NRC tous droits réservés.

The SAFE (sylviculture et aménagement forestiers écosystémique) project was set up in 1998 in the Lake Duparquet Research and Teaching Forest to test stand-level silvicultural treatments designed to reflect different aspects of natural forest dynamics. In the winter of 1998–1999, four levels of forest harvesting, including a no-harvest and a clearcut treatment, were applied to even-aged trembling aspen (Populus tremuloides Michx.) stands according to a complete block design with three replications. Two partial cut treatments removed 33% and 61% of the stand basal area. During the first growing season, harvesting induced a large increase in indigenous understorey biomass that paralleled changes in the canopy opening. Aspen sucker density increased from 4916 stems/ha in the control to 28 751 and 63 333 stems/ha in the one-third and two-thirds harvesting treatments and 102 916 stems/ha in the clearcut. Most changes in nutrient cycling occurred in the second year and included an increase in forest floor organic C, total N, and base cation availability and a decrease in microbial C/N ratio. These changes may have occurred in response to reduced vegetation uptake and woody debris abundance.

Le projet SAFE (sylviculture et aménagement forestiers écosystémique) a débuté en 1998 dans la Forêt d'enseignement et de recherche du lac Duparquet afin de tester différents traitements sylvicoles inspirés de la dynamique naturelle des peuplements. Quatre intensités de récolte, incluant la coupe totale, la récolte de 33 et 61% de la surface terrière totale et un traitement témoin non coupé, ont été appliquées à des peuplements équiennes de tremble (Populus tremuloides Michx.) au cours de l'hiver 1998–1999, selon un plan en block complet avec trois répétitions. La végétation de sous bois a répondu par une augmentation de sa biomasse proportionnelle à l'ouverture du couvert. Au cours de la première année, la densité des drageons de tremble était de 4916 tiges/ha dans le traitement témoin, 28 751 et 63 333 tiges/ha dans les coupes partielles et 102 916 tiges/ha dans la coupe totale. La plupart des changements observés dans le cycle des nutriments sont survenus dans la couverture morte pendant la deuxième année suivant la coupe. Parmi ceux-ci figurent une augmentation du C organique, du N total et des cations basiques échangeables et une diminution du ratio C/N de la biomasse microbienne. La diminution du prélèvement par les plantes et les changements dans l'abondance des débris ligneux expliqueraient ces changements.©2004 NRC Canada

A review of the scientific literature relevant to the Claybelt region was undertaken under the initiative of Lake Abitibi Model Forest (LAMF) and in collaboration with the Canadian Forest Service, the Ontario and Quebec Ministries of Natural Resources and the NSERC-UQAT-UQAM (Natural Sciences and Engineering Research Council - Universite du Quebec en Abitibi-Temiscamingue Universite du Quebec A Montreal) Industrial Chair in Sustainable forest Management. The objective was to synthesize this information in order to develop better forestry practices and identify knowledge and research gaps. Forestry-related knowledge was gathered on six broad topics: i) natural disturbances, ii) forest ecosystems, iii) past and present forest practices, iv) biological diversity, v) forest management and vi) examples of current applications of natural disturbance-based forest management. The work allowed us to synthesize a large body of knowledge into one publication that will be a useful reference for foresters in both provinces.

Forest ecosystem management, based partly on a greater understanding of natural disturbance regimes, has many variations but is generally considered the most promising approach to accommodating biodiversity concerns in managed forested regions. Using the Lake Duparquet Forest in the southeastern Canadian boreal forest as an example, we demonstrate an approach that attempts to integrate forest and stand-level scales in biodiversity maintenance. The concept of cohorts is used to integrate stand age, composition and structure into broad successional or stand development phases. Mean forest age (MFA), because it partly incorporates historic variability of the regional fire cycle, is used as a target fire cycle. At the landscape level, forest composition and cohort objectives are derived from regional natural disturbance history, ecosystem classification, stand dynamics and a negative exponential age distribution based on a 140 year fire cycle. The resulting multi-cohort structure provides a framework for maintaining the landscape in a semi-natural age structure and composition. At the stand level, the approach relies on diversifying interventions, using both even-aged and uneven-aged silviculture to reflect natural stand dynamics, control the passage (‘‘fluxes’’) between forest types of different cohorts and maintain forest-level objectives. Partial and selective harvesting is intended to create the structural and compositional characteristics of mid- to late-successional forest types and, as such, offers an alternative to increasing rotation lengths to maintain ecosystem diversity associated with over-mature and old-growth forests. The approach does not however supplant the necessity for complementary strategies for maintaining biodiversity such as the creation of reserves to protect rare, old or simply natural ecosystems. The emphasis on maintaining the cohort structure and forest type diversity contrasts significantly with current even-aged management in the Canadian boreal forest and has implications for stand-level interventions, notably in necessitating a greater diversification of silvicultural practices including more uneven-aged harvesting regimes. The approach also presents a number of operational challenges and potentially higher risks associated with multiply stand entries, partial cutting and longer intervals between final harvests. There is a need for translating the conceptual model into a more quantitative silvicultural framework. Silvicultural Forest ecosystem management, based partly on a greater understanding of natural disturbance regimes, has many variations but is generally considered the most promising approach to accommodating biodiversity concerns in managed forested regions. Using the Lake Duparquet Forest in the southeastern Canadian boreal forest as an example, we demonstrate an approach that attempts to integrate forest and stand-level scales in biodiversity maintenance. The concept of cohorts is used to integrate stand age, composition and structure into broad successional or stand development phases. Mean forest age (MFA), because it partly incorporates historic variability of the regional fire cycle, is used as a target fire cycle. At the landscape level, forest composition and cohort objectives are derived from regional natural disturbance history, ecosystem classification, stand dynamics and a negative exponential age distribution based on a 140 year fire cycle. The resulting multi-cohort structure provides a framework for maintaining the landscape in a semi-natural age structure and composition. At the stand level, the approach relies on diversifying interventions, using both even-aged and uneven-aged silviculture to reflect natural stand dynamics, control the passage (‘‘fluxes’’) between forest types of different cohorts and maintain forest-level objectives. Partial and selective harvesting is intended to create the structural and compositional characteristics of mid- to late-successional forest types and, as such, offers an alternative to increasing rotation lengths to maintain ecosystem diversity associated with over-mature and old-growth forests. The approach does not however supplant the necessity for complementary strategies for maintaining biodiversity such as the creation of reserves to protect rare, old or simply natural ecosystems. The emphasis on maintaining the cohort structure and forest type diversity contrasts significantly with current even-aged management in the Canadian boreal forest and has implications for stand-level interventions, notably in necessitating a greater diversification of silvicultural practices including more uneven-aged harvesting regimes. The approach also presents a number of operational challenges and potentially higher risks associated with multiply stand entries, partial cutting and longer intervals between final harvests. There is a need for translating the conceptual model into a more quantitative silvicultural framework. SilviculturalForest ecosystem management, based partly on a greater understanding of natural disturbance regimes, has many variations but is generally considered the most promising approach to accommodating biodiversity concerns in managed forested regions. Using the Lake Duparquet Forest in the southeastern Canadian boreal forest as an example, we demonstrate an approach that attempts to integrate forest and stand-level scales in biodiversity maintenance. The concept of cohorts is used to integrate stand age, composition and structure into broad successional or stand development phases. Mean forest age (MFA), because it partly incorporates historic variability of the regional fire cycle, is used as a target fire cycle. At the landscape level, forest composition and cohort objectives are derived from regional natural disturbance history, ecosystem classification, stand dynamics and a negative exponential age distribution based on a 140 year fire cycle. The resulting multi-cohort structure provides a framework for maintaining the landscape in a semi-natural age structure and composition. At the stand level, the approach relies on diversifying interventions, using both even-aged and uneven-aged silviculture to reflect natural stand dynamics, control the passage (‘‘fluxes’’) between forest types of different cohorts and maintain forest-level objectives. Partial and selective harvesting is intended to create the structural and compositional characteristics of mid- to late-successional forest types and, as such, offers an alternative to increasing rotation lengths to maintain ecosystem diversity associated with over-mature and old-growth forests. The approach does not however supplant the necessity for complementary strategies for maintaining biodiversity such as the creation of reserves to protect rare, old or simply natural ecosystems. The emphasis on maintaining the cohort structure and forest type diversity contrasts significantly with current even-aged management in the Canadian boreal forest and has implications for stand-level interventions, notably in necessitating a greater diversification of silvicultural practices including more uneven-aged harvesting regimes. The approach also presents a number of operational challenges and potentially higher risks associated with multiply stand entries, partial cutting and longer intervals between final harvests. There is a need for translating the conceptual model into a more quantitative silvicultural framework. Silvicultural trials have been established to evaluate stand-level responses to treatments and operational aspects of the approach. © 2002 Elsevier B.V. All rights reserved.

The combination of certain features of fire disturbance, notably fire frequency, size and severity, may be used to characterize the disturbance regime in any region of the boreal forest. As some consequences of fire resemble the effects of industrial forest harvesting, conventional forest management is often considered as a disturbance that has effects similar to those of natural disturbances. Although the analogy between forest management and are disturbance in boreal ecosystems has some merit, it is important to recognise that it also has its limitations. Short fire cycles generally described for boreal ecosystems do not appear to be universal rather, important spatial and temporal variations have been observed in Canada. These variations in the fire cycle have an important influence on forest composition and structure at the landscape and regional levels. Size and severity of fires also show a large range of variability. In regions where the natural matrix of the boreal forest remains relatively intact, maintenance of this natural variability should be targeted by forest managers concerned with biodiversity conservation. Current forest management tends to reduce this variability: for example, fully regulated, even-aged management will tend to truncate the natural forest age distribution and eliminate over-mature and old-growth forests from the landscape. We suggest that the development of strategic-level forest management planning approaches and silvicultural techniques designed to maintain a spectrum of forest compositions and structures at different scales in the landscape is one avenue to maintain this variability. Although we use the boreal forest of Quebec for our examples, it is possible to apply the approach to those portions of the boreal forest where the fire regime favours the development of even-aged stands in burns.

Careful logging regulations in Quebec restrict circulation of harvesting and forwarding or skidding machinery to evenly spaced, parallel trails, which creates a particular pattern of disturbed and relatively undisturbed zones in cutovers. A 7-year monitoring study was established to evaluate the effects of careful logging on vegetation development in the southern boreal forest of Quebec. A total of 255 sample plots (2 m²) were located in seven cutovers in predominantly black spruce (Picea mariana (Mill.) BSP) forests that were whole-tree "careful logged": 120 on fresh to moist silty clays or silty clay loams and 135 on dry to fresh loamy sands. Three microsites were sampled: skid trails and the edge and the centre of protection strips. A gradient of disturbance from the skid trail to centre of the protection strip was evident for finer textured sites. Careful logging resulted in high densities of black spruce and balsam fir (Abies balsamea (L.) Mill.) (> 20 000 stems/ha each) in the protection strip. Survival of other understory species was also favoured in protection strips. Higher disturbance levels in skid trails favoured establishment of larch (Larix laricina (Du Roi) K. Koch), raspberry (Rubus idaeus L.), and graminoids. Reduction of ericaceous cover occurred in skid trails on coarse-textured sites but was only temporary. Softwood stocking 7 years after harvest (based on 2-m² plots), ranged from 69 to 74% on fine- to medium-textured sites and from 31 to 51% on coarse-textured sites. The pattern of vegetation development created by careful logging has important implications for silvicultural decisions and stand modelling.©2002 NRC Canada

The Lake Duparquet Research and Teaching Forest is situated in northwestern Quebec in the Boreal Shield Ecozone. Managed by two constituents of the Universite du Quebec, in collaboration with two forest companies, Norbord and Tembec, the Lake Duparquet Forest has a strong research program focussed on natural forest ecosystem dynamics that provides the scientific basis for management and silvicultural trials recently begun in the Forest. A bibliographical review of research activities is presented.

Although the concept of forest ecosystem management based on natural disturbance has generated a great deal of interest, few concrete examples exist of FEM principles being put into application. Silvicultural practices that emulate natural disturbances are proposed with examples from the principal vegetation zones of Quebec. With the exception of the large-scale use of careful logging to protect advanced regeneration in ecosystems generally controlled by fire, stand-level silvicultural practices currently used are reasonably similar to natural disturbances, although important differences exist. In contrast, at the forest-level, even-aged management as is currently practised rarely permits adequate reproduction of the variety of age classes, stand types, and structural components normally found in the boreal forest. A model that allows an even-aged management approach inspired by natural dynamics is proposed.

Although the concept of forest ecosystem management based on natural disturbance has generated a great deal of interest, few concrete examples exist of FEM principles being put into application. Silvicultural practices that emulate natural disturbances are proposed with examples from the principal vegetation zones of Quebec. With the exception of the large-scale use of careful logging to protect advanced regeneration in ecosystems generally controlled by fire, stand-level silvicultural practices currently used are reasonably similar to natural disturbances, although important differences exist. In contrast, at the forest-level, even-aged management as is currently practised rarely permits adequate reproduction of the variety of age classes, stand types, and structural components normally found in the boreal forest. A model that allows an even-aged management approach inspired by natural dynamics is proposed.

We present a method in which fundamental knowledge of natural ecosystem dynamics of the southern boreal forest may be used as a basis for a new silvicultural approach aimed at maintaining biodiversity and long-term ecosystem productivity under management. The natural disturbance regime of the southern boreal forest of Quebec is characterized by intense crown fires. Natural forest dynamics following fire on mesic sites involve a gradual replacement of stands of broadleaf species by mixedwood then softwood stands. This succession is accompanied by a decrease in soil fertility and in ecosystem productivity. In the absence of fire, spruce budworm outbreaks contribute in regenerating mature, fir-dominated forests and in reintroducing a hardwood component into stands. Current silvicultural practices promote successive rotations of similarly composed stands. Attaining softwood regeneration following harvest of softwood stands often necessitates site preparation, planting and control of competitive species, including economically and ecologically valuable hardwoods. At the landscape level this strategy may contribute to decreasing stand diversity by favouring replacement of mixedwood stands by hardwood or softwood stands. Natural dynamics indicate that a silvicultural approach favouring species replacement while, at the landscape level preserving a representative proportion of hardwood, mixedwood and softwood stands would be more appropriate. The advantages of such an approach are discussed in comparison with current practices. © 1997 Elsevier B.V. All rights reserved.

In Quebec, forest stations are defined as forest units that are reasonably homogeneous in terms of forest composition and site characteristics - as expressed by surficial deposit and moisture regime - and within which similar operational constraints for silvicultural potential and productivity levels may be expected. In the course of developing a field guide to the forest stations of the Amos Lowlands Ecological Region in northwestern Quebec, classifications of 12 site types and 72 forest stations (38 forest cover types or 16 general cover types) were developed. The classifications were based on a hybrid approach involving cluster analysis of forest ecological units inventoried in subregional studies, classical classification and ordination analyses performed on a regional biophysical inventory database, and empirically associating forest cover types to site types. The guide, while similar to other published forest ecosystem classification guides, emphasizes forest dynamics by presenting forest stations common to a given site type according to their successional stage. Field keys and general interpretations of forest potential and operational constraints are included in the guide. A summary description of the guide and accompanying documents is provided. A first draft has been distributed recently for feedback from industrial and government foresters and researchers in the region. Analyses of inventory data is continuing and modifications will be incorporated into a second draft before publication in 1995.

Abstract:

Early vegetation development following harvest was evaluated for nine common site types in the southern clay belt of northwestern Quebec. Stocking of broadleaf tree and high shrub stems less than 1 m tall was either stable or declined on all sites over a period of 8 years following harvest, whereas stocking of stems over 1 m displayed increases on all but mesic clay sites. These latter sites had the lowest broadleaf and high shrub stocking but a high cover of raspberry (Rubusidaeus L.), low shrubs, and herbs. Mesic to hydric clays and hydric organic site types had considerably higher cover of ruderal and introduced species than sand and till sites, TWINSPAN indicator species analysis was used to explore phytosociological associations of postharvest vegetation. The distribution of 11 phytosociological groups among the nine site types was analysed using contingency analysis to test the specificity of species groups to site types and the floristic amplitude of the latter. With the exception of one phytosociological group that displayed a broad spectrum of site type occupation, these groups tended to be associated with sites of similar soil moisture regimes and (or) parent material types. While site type may be improved upon as a stratifier by integrating other environmental, biotic, and operational variables, it does appear to provide a good initial basis for stratification in studies of postdisturbance vegetation dynamics.

Résumé:

Nous avons évalué le développement végétal après la récolte sur neuf sites forestiers de la ceinture d'argile du nord-ouest québécois. Le coefficient de distribution (CD) des tiges de moins de 1 m de feuillus et d'arbustes hauts était stable ou diminuait sur une période de 8 ans après coupe et ceci sur tous les sites, tandis que le CD des tiges plus hautes que 1 m augmentait sur tous les sites à l'exception des sites sur argile mésique. Ces derniers avaient le CD des feuillus et des arbustes hauts le plus bas mais des recouvrements élevés de framboisier (Rubusidaeus L.), d'arbustes bas et d'herbacées. Les sites sur argile mésique à hydrique et sur matière organique hydrique montraient des recouvrements plus importants d'espèces rudérales et introduites relativement aux sites sur sable ou sur till. Onze associations phytosociologiques ont, par ailleurs, été identifiées à l'aide de l'analyse d'espèces indicatrices TWINSPAN afin d'explorer des associations phytosociologiques dans la végétation post-récolte. La distribution de ces groupes parmi les sites forestiers a été analysée à l'aide de tableaux de contingence dans le but de vérifier la spécificité des groupes phytosociologiques selon les sites forestiers ainsi que l'amplitude floristique de ces derniers. À l'exception d'un groupe phytosociologique qui présentait un large spectre d'occupation parmi les sites, ces groupes avaient tendance à s'associer aux sites forestiers de régime hydrique et (ou) de dépôt de surface semblables. Bien que le site forestier puisse être amélioré, en tant que stratificateur, en intégrant des variables environnementales, biotiques et opérationnelles, il semble fournir une première base de stratification intéressante pour des études sur la dynamique végétale après perturbation. ©1995 NRC Canada

The Quebec Ministry of Forests has developed an approach to ecological cartography designed to complement its traditional forest inventory and delimit homogeneous land units for forest management. The methodology consists of field work, map analysis and photointerpretation. Within the hierarchical classification, ecological regions reflecting regional climate are mapped at the 1:1 250 000 scale. Major physiographic ensembles and ecological districts, mapped at 1:250 000, express patterns of physiography, geology and geomorphology and ecological types (1:20 000) characterize surface deposits, drainage class, slope and potential climax forest. Using information drawn from ecological classification work in northwestern Quebec and applying the Ministry's standards, an ecological framework for two townships was developed. In addition to maps of each classification level, the framework includes interpretative documents such as schematic cross-sections of ecosystems and descriptive texts. Examples of management interpretations (natural regeneration potential and site preparation effect on competition) are presented. The classification approach and its future are evaluated.

Le Ministère des Forêts du Québec a développé une approche de cartographie écoligique destinée à être le complément de l'inventaire forestier traditionnel et visant la délimitation de superficies homogènes sur le plan de l'aménagement. La méthode comprend: travaux sur le terrain, analyses de cartes et de photos aériennes. Le premier niveau de la classification hiérarchique (régions écologiques, 1:1 250 000) représente les variations du climat régional. Les ensembles physiographiques et districts écologiques (1:250 000) montrent l'agencement du relief, de la géologie et de la géomorphologie et les types écologiques (1:20 000) sont caractérisés par leur dépot de surface, drainage, pente et végétation de fin de succession. Des travaux de classification écologique réalisés au nord-ouest du Québec, ont permits cartographier deux cantons selon les normes du MFO. Le cadre écologique forestier. © 1992 Elsevier B.V. All rights reserved.

Abstract

Pre- and post-harvest regeneration levels were compared for Abiesbalsamea (L.) Mill. –Betulapapyrifera Marsh. –Picea spp. forests in an area of the southern clay belt of northwestern Quebec. Results revealed abundant advance softwood regeneration (mean = 65 000 stems/ha), almost entirely of Abies prior to harvest. The survey following mechanical and manual whole-tree harvesting suggested a 92% reduction of softwood regeneration and a shift from softwood to a mixed or hardwood-shrub dominated regeneration. Ninety percent of softwood seedlings collected after harvest were pre-established. Destruction of advance regeneration was generally greater on fine-textured soils. Hierarchic cluster analysis of ecological types based on softwood, hardwood, and shrub tree regeneration data as variables, revealed nine groups that could serve as a basis for operational silvicultural decision making. In general, Salix spp. and Alnusrugosa (Du Roi) Spreng. are the major competitors on poorly drained sites; Betula sp., Acerspicatum Lam., and Prunuspensylvanica L.f. dominate on thin organic deposits and coarse deposits, whereas Populustremuloides Michx. and Acerspicatum dominate on fine-textured deposits. These findings suggest that a good understanding of physical site factors can provide useful information for harvesting and silvicultural planning.

Résumé:

L'abondance de la régénération avant et après coupe a été comparée pour un ensemble forestier dominé par Abiesbalsamea (L.) Mill., Betulapapyrifera Marsh, et Picea spp. situé dans la portion sud de la ceinture d'argile au nord-ouest du Québec. Les résultats montrent que la régénération en espèces conifériennes avant la coupe était abondante (moyenne = 65 000 tiges/ha) et qu'elle était surtout composée d'Abies. La situation après coupe suggère une réduction de la densité des espèces conifériennes de l'ordre de 92%, occasionnant le passage d'une régénération avant coupe dominée par les conifères vers une composition après coupe mixte ou dominée par les feuillus. Quatre-vingt-dix pour cent des semis prélevés après coupe mécanique et manuelle à l'arbre entier étaient préétablis. La destruction de la régénération préétablie était généralement plus importante sur les sites à texture fine. Un regroupement des types écologiques à l'aide d'une analyse par agglomération hiérarchique, basée sur la régénération résineuse, et la compétition par les espèces feuillues, a permis de mettre en évidence neuf «unités de traitement» qui peuvent servir de base opérationnelle de décision pour les traitements sylvicoles. En général, Salix spp. et Alnusrugosa (Du Roi) Spreng. constituent le principal problème sylvicole sur les sites mal drainés, Betula sp., Acerspicatum Lam. et Prunuspensylvanica L.f. dominent sur les dépôts organiques minces et les dépôts grossiers alors que Populustremuloides Michx. et Acerspicatum sont les principaux compétiteurs sur les dépôts à textures fines. Les résultats confirment l'importance d'une bonne connaissance des facteurs physiques du milieu dans la planification des interventions sylvicoles et de récolte. ©1989 NRC Canada